1. Field of the Invention
The present invention relates to an electro-conductive member, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
In an electrophotographic image-forming apparatus, an electro-conductive member has been used in various fields such as a charging roller, a developing roller, and a transfer roller. The resistance value of such electro-conductive member preferably falls within the range of 103 to 1010Ω. Accordingly, the conductivity of an electro-conductive layer which the electro-conductive member includes has been adjusted with an electro-conductive agent. Here, the electro-conductive agents are roughly classified into an electronic electro-conductive agent typified by carbon black and an ionic electro-conductive agent such as a quaternary ammonium salt compound. Those electro-conductive agents each have an advantage and a disadvantage.
An electro-conductive layer that has been made conductivity with the electronic electro-conductive agent such as carbon black shows a small change in resistance value with a use environment. In addition, the electronic electro-conductive agent hardly bleeds to the surface of the electro-conductive layer, and hence there is a small possibility that the agent contaminates the surface of a member on which an electro-conductive member including such an electro-conductive layer abuts, e.g., an electrophotographic photosensitive member (hereinafter referred to as “photosensitive member”). However, it is difficult to uniformly disperse the electronic electro-conductive agent in a binder resin and hence the electronic electro-conductive agent is liable to agglomerate in the electro-conductive layer. Accordingly, local unevenness of the resistance value may occur in the electro-conductive layer.
On the other hand, in the case of an electro-conductive layer that has been made conductivity with the ionic electro-conductive agent, the ionic electro-conductive agent is uniformly dispersed in a binder resin as compared with the electronic electro-conductive agent. Accordingly, local resistance unevenness hardly occurs in the electro-conductive layer. However, the ion-conducting performance of the ionic electro-conductive agent is susceptible to the amount of moisture in the binder resin under a use environment. Accordingly, the resistance value of the electro-conductive layer that has been made conductivity with the ionic electro-conductive agent increases under a low-temperature, low-humidity environment (having a temperature of 15° C. and a relative humidity of 10%) (hereinafter sometimes referred to as “L/L environment”), and reduces under a high-temperature, high-humidity environment (having a temperature of 30° C. and a relative humidity of 80%) (hereinafter sometimes referred to as “H/H environment”). That is, the electro-conductive layer involves a problem in that the environmental dependence of its resistance value is large.
Further, when a direct-current voltage is applied to an electro-conductive member including the electro-conductive layer that has been made conductivity with the ionic electro-conductive agent over a long time period, the following tendency has been observed. A cation and anion constituting the ionic electro-conductive agent are polarized in the electro-conductive layer, an ion density in the electro-conductive layer reduces, and the resistance value of the electro-conductive layer gradually increases.
Japanese Patent Application Laid-Open No. 2000-186129 proposes that an ionic functional group be introduced into a molecular structure of a silicone-modified urethane polymer to impart charge-removing property to the polymer itself instead of a charge-removing method using an electro-conductive agent such as carbon powder.